Measurements and modeling of absorption by CO2+H2O mixtures in the spectral region beyond the CO2 nu3-band head

TL;DR

This study measures and models the absorption of CO2+H2O mixtures beyond the CO2 nu3-band head, revealing a significant water vapor continuum that impacts radiative transfer calculations.

Contribution

It provides new high-resolution measurements and an empirical model for CO2+H2O absorption beyond the nu3-band head, improving accuracy in atmospheric radiative transfer modeling.

Findings

Water vapor significantly increases the CO2 continuum absorption.

The empirical model accurately describes the measured absorption spectra.

Results agree with previous measurements in a narrower spectral range.

Abstract

In this work, we measured the absorption by CO2+H2O mixtures from 2400 to 2600 cm-1 which corresponds to the spectral region beyond the nu3 band head of CO2. Transmission spectra of CO2 mixed with water vapor were recorded with a high-resolution Fourier-transform spectrometer for various pressure, temperature and concentration conditions. The continuum absorption by CO2 due to the presence of water vapor was determined by subtracting from measured spectra the contribution of local lines of both species, that of the continuum of pure CO2 as well as of the self- and CO2-continua of water vapor induced by the H2O-H2O and H2O-CO2 interactions. The obtained results are in very good agreement with the unique previous measurement (in a narrower spectral range). They confirm that the H2O-continuum of CO2 is significantly larger than that observed for pure CO2. This continuum thus must be taken into account in radiative transfer calculations for media involving CO2+H2O mixture. An empirical model, using sub-Lorentzian line shapes based on some temperature-dependent correction factors chi is proposed which enables an accurate description of the experimental results.